Aircraft positioning method based on SAR image scene matching

Abstract

The invention belongs to the technical field of aircraft integrated navigation and positioning, particularly relates to an aircraft positioning method based on SAR image scene matching, and aims to solve the problems that satellite positioning fails, the positioning error of an inertial navigation system is gradually increased during long-time long-distance navigation of an aircraft, and accurate positioning of the aircraft is difficult to realize. The advantages of all-time all-weather long-distance work, high-precision distance and angle measurement, strong anti-interference capability and the like of the SAR are exerted, high-precision inversion of aircraft coordinates is realized by adopting methods of scene matching based on SAR images, imaging parameter estimation, multi-stage coordinate system conversion and the like, and high-precision positioning of the aircraft is realized. The method has great application potential in the fields of navigation positioning, reconnaissance monitoring and the like.

Description

Technical Field

[0001] The present application belongs to the technical field of aircraft integrated navigation and positioning, and specifically relates to an aircraft positioning method based on SAR image scene matching. Background Art

[0002] The navigation and positioning of aircraft during navigation is an important issue that needs to be solved during engineering implementation, especially the navigation and positioning of long-duration flying aircraft such as medium- and long-range UAVs, which requires autonomy that does not rely on external information.

[0003] The inertial navigation system (INS) has strong anti-interference ability and can work all-weather, but its accuracy is not high, and the navigation error will accumulate over time. Satellite navigation mainly includes the Global Positioning System and the Beidou Satellite Navigation System, which have high accuracy and the error does not accumulate over time, but are easily affected by current politics and signal interference.

[0004] At present, the integrated navigation system usually combines INS and satellite navigation to make full use of their respective advantages and improve positioning accuracy. However, when the satellite signal fails, the navigation information error obtained by the inertial navigation system alone will continue to increase, and the aircraft will face risks, which does not meet the autonomous navigation requirements in complex electromagnetic environments.

[0005] Synthetic aperture radar (SAR) is not only used as a mission payload for aircraft to perform intelligence reconnaissance and surveillance tasks, but also can use the real-time measured ground SAR images to match the built-in reference images, provide accurate position information for aircraft, correct the error accumulation of the inertial navigation system due to accelerometer errors and gyroscope drift, and improve the accuracy of autonomous navigation. SAR has the advantages of all-weather, high accuracy, and strong autonomy.

[0006] INS / SAR or INS / satellite / SAR integrated navigation system is a new type of integrated navigation system with strong practicality. Figure 1 As shown. SAR completes SAR imaging, scene matching, and aircraft positioning in sequence, and inputs the aircraft position information into the combined navigation filter to achieve INS / satellite / SAR combined navigation. INS outputs the aircraft position, speed, and attitude information containing time-accumulated errors to SAR for imaging processing to obtain real-time SAR images, which are scene matched with the built-in reference image. The image coordinates are obtained based on the matching results, and the accurate position of the aircraft is calculated by combining the image coordinates and the aircraft positioning method. The aircraft position measured by INS is compared with the position output by SAR and the error is corrected. The real-time and accurate position information of the aircraft is obtained by the combined navigation filter to achieve high-precision navigation and positioning. Since SAR image scene matching can only obtain image latitude and longitude, without altitude information, a radio altimeter or a barometric altimeter is required to provide the aircraft altitude for aircraft positioning.

[0007] INS / SAR or INS / satellite / SAR combined navigation system uses the positioning results of SAR image scene matching to correct INS, overcoming the shortcoming that its error increases with time. At the same time, the aircraft speed obtained by INS is used to perform motion compensation on SAR imaging, and the output aircraft attitude is used to stabilize the radar antenna beam in the airspace. The combination of INS and SAR can complement each other.

[0008] Navigation positioning based on SAR image scene matching is a key technology of INS / SAR or INS / satellite / SAR combined navigation system. Current research on it focuses on matching methods based on traditional image features or image matching methods based on deep learning, while there is less research on methods for aircraft positioning after image matching. The relevant technical solutions are immature and difficult to apply. In view of this, this application is proposed.

[0009] This application is proposed in view of the above-mentioned technical defects. Summary of the invention

[0010] The purpose of this application is to provide an aircraft positioning method based on SAR image scene matching to address the problem that the cumulative error of the inertial navigation system gradually increases when the aircraft is flying for a long time and over a long distance, and in extreme cases, the satellite positioning data cannot be obtained for correction, making it impossible to complete high-precision navigation and positioning. The method can give full play to the SAR's all-weather and all-day working capabilities, use the aircraft's built-in reference image to match the real-time SAR image, combine the speed, angle, distance and other parameters measured by the radar with the imaging geometry model, build an aircraft positioning model, and achieve high-precision positioning of the aircraft through a series of coordinate transformations and track angle estimation methods.

[0011] The technical solution of this application is:

[0012] An aircraft positioning method based on SAR image scene matching, comprising:

[0013] Step 1: scene matching is performed between the real-time SAR image and the built-in reference image to obtain the pixel position and latitude and longitude coordinates of the scene matching feature points in the SAR image;

[0014] Step 2: Calculate the coordinates of the aircraft in the earth coordinate system based on the pixel positions and longitude and latitude coordinates of the scene matching feature points;

[0015] Step 3: The coordinates of the aircraft in the earth coordinate system are calculated to calculate the longitude and latitude coordinates of the aircraft and realize the positioning of the aircraft.

[0016] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, in step one, scene matching is performed on the real-time SAR image and the built-in reference image through a traditional image feature matching method or an image matching method based on deep learning.

[0017] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, the reference image includes a high-precision digital map, an airborne / satellite-borne reference map, a homologous / heterogeneous SAR image, and an optical image.

[0018] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, in step 2, when calculating the coordinates of the aircraft in the earth coordinate system according to the pixel position and longitude and latitude coordinates of the scene matching feature point, when there is only one scene matching feature point, calculating the coordinates of the aircraft in the earth coordinate system includes:

[0019] S11, calculate the coordinates of the scene matching feature points in the image coordinate system [X i ,Y i ,Z i ] T :

[0020]

[0021]

[0022] in,

[0023] p r is the SAR image distance pixel size;

[0024] p a is the SAR image azimuth pixel size;

[0025] N r is the number of points in the range direction of the SAR image;

[0026] N a is the number of SAR image azimuth points;

[0027] (n r ,n a ) is the pixel position of the scene matching feature point;

[0028] DirectionFlag is the SAR left / right viewing imaging direction;

[0029] S12, calculate the coordinates of the scene matching feature points in the imaging coordinate system [X p ,Y p ,Z p ] T :

[0030]

[0031] in,

[0032] θ ac is the imaging azimuth of the aperture center, -180°≤θ ac ≤180°, right side is considered positive;

[0033] H e is the height of the aircraft relative to the ground;

[0034] R c is the action distance;

[0035] S13, calculate the coordinates of the scene matching feature points relative to the aircraft in the geographic coordinate system [X E ,Y N ,Z S ] T :

[0036]

[0037] in,

[0038] θ track is the track angle;

[0039] S14, calculate the coordinates of the scene matching feature points in the earth coordinate system [x e ,y e ,z e ] T :

[0040]

[0041]

[0042] in,

[0043] R e is the equatorial plane radius;

[0044] e eccentricity;

[0045] N is the radius of the Maoyou circle;

[0046] β is the latitude of the scene matching feature point;

[0047] α is the longitude of the scene matching feature point;

[0048] S15, calculate the coordinates of the scene matching feature points relative to the aircraft in the earth coordinate system [△X e ,△Y e ,△Z e ] T :

[0049]

[0050] S16. Calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T :

[0051]

[0052] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, in step 2, when calculating the coordinates of the aircraft in the earth coordinate system according to the pixel position and the latitude and longitude coordinates of the scene matching feature point, when there are two or more scene matching feature points, two points are selected, scene matching feature point 1 and scene matching feature point 2, to calculate the coordinates of the aircraft in the earth coordinate system:

[0053] S21, calculate the coordinates [x e1 ,y e1 ,z e1 ] T and [x e2 ,y e2 ,z e2 ] T :

[0054]

[0055]

[0056] in,

[0057] h1 is the ellipsoid height of scene matching feature point 1;

[0058] β1 is the latitude of scene matching feature point 1;

[0059] α1 is the longitude of scene matching feature point 1;

[0060] h2 is the ellipsoid height of scene matching feature point 2;

[0061] β2 is the latitude of scene matching feature point 2;

[0062] α2 is the longitude of scene matching feature point 2;

[0063] S22, calculate the coordinates [x e12 ,y e12 ,z e12 ] T ;

[0064]

[0065] S23, calculate the coordinates [X] of scene matching feature point 2 relative to scene matching feature point 1 in the geographic system. E12 ,Y N12 ,Z S12 ] T :

[0066]

[0067] S24, calculate the rotation angle (θ track +θ ac ):

[0068]

[0069]

[0070] [X i12 ,Y i12 ,Z i12 ] T is the coordinate of scene matching feature point 2 relative to scene matching feature point 1 in the image coordinate system;

[0071] (nr1, na1) is the pixel coordinate of scene matching feature point 1;

[0072] (nr2, na2) is the pixel coordinate of scene matching feature point 2;

[0073] S25, calculate the coordinates of the scene matching feature point 1 relative to the aircraft in the geographic system [X E01 ,Y N01 ,Z S01 ] T :

[0074]

[0075]

[0076] in,

[0077] [X i1 ,Y i1 ,Z i1 ] T is the coordinate of scene matching feature point 1 in the image coordinate system;

[0078] S26, calculate the coordinates of the aircraft relative to the scene matching feature point 1 in the earth coordinate system [△X e1 ,△Y e1 ,△Z e1 ]T :

[0079]

[0080] S27, calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T :

[0081]

[0082] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, R e =6378137m.

[0083] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, e 2 =0.006694379995.

[0084] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, in step 3, the longitude and latitude coordinates of the aircraft are calculated based on the coordinates of the aircraft in the earth coordinate system, and the longitude α of the aircraft is calculated. T Calculated as:

[0085] α T =arctan(Y e ,X e ).

[0086] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, in step 3, the latitude β of the aircraft is calculated by using the coordinates of the aircraft in the earth coordinate system to calculate the latitude and longitude coordinates of the aircraft. T , height H T Calculated as:

[0087] N, H T Assign initial value and iteratively calculate the latitude β of the aircraft T , height H T , when the latitude β of the aircraft calculated in two consecutive iterations T When the difference is less than the set threshold, the iteration stops and the latitude β of the aircraft is obtained. T , height H T , the iterative process is:

[0088]

[0089]

[0090]

[0091] According to at least one embodiment of the present application, in the above-mentioned aircraft positioning method based on SAR image scene matching, the threshold is set to 1e-10.

[0092] This application has at least the following beneficial technical effects:

[0093] The invention provides an aircraft positioning method based on SAR image scene matching. In order to solve the problem that satellite positioning fails and the positioning error of the inertial navigation system gradually increases when the aircraft flies for a long time and over a long distance, it is difficult to accurately position the aircraft. By giving full play to the advantages of SAR itself, such as all-day and all-weather long-distance operation, high-precision ranging and angle measurement, and strong anti-interference ability, the method of scene matching based on SAR images, imaging parameter estimation, multi-level coordinate system conversion and other methods are adopted to realize high-precision inversion of aircraft coordinates and high-precision positioning of aircraft. The method has great application potential in the fields of navigation positioning, reconnaissance and surveillance. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 It is a schematic diagram of the INS / satellite / SAR integrated navigation system;

[0095] Figure 2 It is a schematic diagram of the relationship between the earth coordinate system, geographic coordinate system, imaging coordinate system, and image coordinate system provided in the embodiment of the present application;

[0096] Figure 3 is a schematic diagram of a geometric model of SAR imaging provided in an embodiment of the present application;

[0097] Figure 4 It is a schematic diagram of an aircraft positioning method based on SAR image scene matching provided in an embodiment of the present application.

[0098] In order to better illustrate the present embodiment, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product. In addition, the drawings are only used for illustrative purposes and should not be construed as limitations on the present application. DETAILED DESCRIPTION

[0099] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present application will be described in further detail in detail and in detail with reference to the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present application, which are only used to explain the present application, not to limit the present application. It should be noted that, for the convenience of description, only the parts related to the present application are shown in the accompanying drawings, and other related parts can refer to the general design.

[0100] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of this application shall have the usual meanings understood by those of ordinary skill in the art to which this application belongs. The words used in the description of this application to indicate orientation are only used to indicate relative directions or positional relationships. When the absolute position of the described object changes, its relative positional relationship may also change accordingly. The word "include" used in the description of this application indicates that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but does not exclude other elements or objects.

[0101] In addition, it should be noted that, unless otherwise clearly specified and limited, the words "installation", "connection" and similar terms used in the description of this application should be understood in a broad sense. For example, the connection can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Technical personnel in the field can understand its specific meaning in this application according to the specific circumstances.

[0102] The embodiment of the present application provides an aircraft positioning method based on SAR image scene matching, which uses the real-time acquired SAR image to match with the built-in reference map, combines imaging parameters and coordinate system conversion principles, realizes the inversion of the aircraft position, and realizes high-precision positioning of the aircraft.

[0103] The aircraft positioning method based on SAR image scene matching provided in the embodiment of the present application involves the transformation of the earth system, geographical system, imaging system, and image system. The coordinate system is as follows: Figure 2 shown.

[0104] Earth coordinate system, the origin of the coordinate system is at the center of the earth O e O e X e The axis points to the starting meridian in the equatorial plane (usually the meridian of the Greenwich Observatory), O e Z e The axis is perpendicular to the equatorial plane and points to the North Pole. e Y e The axis is determined by the right-hand rule. α is longitude and β is latitude.

[0105] The geographic coordinate system adopts the Northeastern Sky (ENS) coordinate system commonly used in my country's inertial navigation system as the geographic coordinate system. The origin O is located at the center of mass of the carrier, OX E Axis points to geographic east, OY N Axis points to geographic north, OZ S Axis vertical OX E Y N The face points toward the zenith.

[0106] Imaging coordinate system, the coordinate system for synthetic aperture imaging processing. The origin of the imaging coordinate system O is located at the center of the synthetic aperture, OX p Axis pointing perpendicular to the track direction, OY p The axis direction is consistent with the flight direction of the aircraft, OZ p Axis vertical OX p Y p The horizontal plane points to the zenith.

[0107] Image coordinate system, the origin O of the image coordinate system is located at the center of the image, O i X i The axis points to the distance dimension of the image, usually the horizontal direction of the image; i Y i The axis points to the azimuth dimension of the image, usually the vertical direction of the image; i Z i Axis vertical O i X i Y i The horizontal plane points to the zenith.

[0108] The geometric model of SAR imaging, such as Figure 3 shown.

[0109] Point A represents the position of the aircraft at the start of a frame of SAR imaging, point B represents the position of the aircraft at the end of imaging, and AB is the length of the synthetic aperture. The origin O in the geographic coordinate system is located at the center of mass of the aircraft at the center of the aperture, OX E Axis points to geographic east, OY N Axis points to geographic north, OZ S The axis points to the zenith. The track angle of the aircraft during synthetic aperture time is θ track (range ±180°, right side is positive), set the center of synthetic aperture to the origin O of imaging coordinate system, imaging coordinate system OX p Axis pointing perpendicular to the track direction, OY p The axis direction is consistent with the flight direction of the aircraft, OX p Y p The surface is parallel to the ground, OZ p Axis vertical OX p Y p The horizontal plane points to the zenith. Imaging coordinate system OX p Y p Z p With geographic coordinate system OX E Y N Z S Phase difference counterclockwise rotation angle θ track .

[0110] Point C is the position point where the aircraft point O is projected onto the ground. i Point is the center of the imaging area, θs is the imaging oblique angle (flight direction is 0°), θ ac is the imaging azimuth of the aperture center (range ±180°, right side is positive), He is the height of the aircraft relative to the ground, and Rc is the slant distance from the aircraft to the center of the imaging area at the aperture center. In the PFA imaging algorithm, Rc is the effective distance. The SAR image obtained by the PFA imaging algorithm is located in the line of sight, and the O of the image coordinate system i X i The axis direction is the line of sight of Rc projected to the ground, that is, the distance direction; perpendicular to O i X i Axis is O i Y i Axis direction, i.e. azimuth; O i Z i The axis points to the zenith and at close range is aligned with OZ S Axis(OZ p axis) directions are approximately the same.

[0111] The pixel display of the image corresponds one-to-one to the image matrix, with pixel (0, 0) at the upper left corner. The azimuth Doppler frequency of the SAR image increases as the pixel number increases.

[0112] The present application embodiment provides an aircraft positioning method based on SAR image scene matching, such as Figure 4 As shown, it mainly involves the processes of scene matching, calculation of aircraft earth system coordinates, and conversion of aircraft latitude and longitude.

[0113] Step 1: Perform scene matching on the real-time SAR image and the built-in reference image to obtain the pixel position and latitude and longitude coordinates of the scene matching feature points in the SAR image.

[0114] The real-time SAR image can be matched with the built-in reference image through traditional image feature matching methods or deep learning-based image matching methods. The reference image can be a high-precision digital map, airborne / satellite-borne reference image, homologous / heterogeneous SAR image, optical image, etc. The reference image has its own longitude and latitude information. After the scene matching is completed, the longitude and latitude coordinates of the corresponding scene matching feature points in the SAR image and their pixel positions in the image can be obtained.

[0115] Step 2: Calculate the coordinates of the aircraft in the earth coordinate system based on the pixel positions and longitude and latitude coordinates of the scene matching feature points.

[0116] The coordinates of the aircraft in the earth coordinate system can be obtained by using the latitude and longitude of the scene matching feature points and the pixel position of the scene matching feature points in the image, combined with the distance, altitude, oblique angle, track angle and other parameters used in imaging, through coordinate system conversion, track angle estimation and correction and other methods.

[0117] When calculating the coordinates of the aircraft in the earth coordinate system, different solution strategies can be used for the case of one or more scene matching feature points.

[0118] When there is only one scene matching feature point, the process of calculating the coordinates of the aircraft in the earth coordinate system can be referred to as follows:

[0119] S11, calculate the coordinates of the scene matching feature points in the image coordinate system [X i ,Y i ,Z i ] T .

[0120]

[0121]

[0122] in,

[0123] p r is the SAR image distance pixel size;

[0124] p a is the SAR image azimuth pixel size;

[0125] N r is the number of points in the range direction of the SAR image;

[0126] N a is the number of SAR image azimuth points;

[0127] (n r ,n a ) is the pixel position of the scene matching feature point;

[0128] DirectionFlag is the SAR left / right viewing imaging direction.

[0129] S12, calculate the coordinates of the scene matching feature points in the imaging coordinate system [X p ,Y p ,Z p ] T .

[0130] The origin of the imaging coordinate system is the aperture center, which also represents the location of the aircraft. Therefore, the coordinates of the scene matching feature point in the imaging coordinate system are [X p ,Y p ,Z p ] T It is also the coordinate of the scene matching feature point relative to the aircraft in the imaging coordinate system.

[0131]

[0132] in,

[0133] θ ac is the imaging azimuth of the aperture center, -180°≤θ ac ≤180°, right side is considered positive;

[0134] H e is the height of the aircraft relative to the ground;

[0135] R c is the action distance.

[0136] S13, calculate the coordinates of the scene matching feature points relative to the aircraft in the geographic coordinate system [X E ,Y N ,Z S ] T .

[0137]

[0138] in,

[0139] θ track is the track angle, which represents the angle between the aircraft's flight direction and the true north direction. The aircraft's geographic coordinate system OX E Y N Z S and imaging coordinate system OX p Y p Z p There is only θ track Angle of rotation.

[0140] S14, calculate the coordinates of the scene matching feature points in the earth coordinate system [x e ,y e ,z e ] T .

[0141]

[0142]

[0143] in,

[0144] R e is the equatorial plane radius. Under the WGS84 earth ellipsoid model, R e =6378137m;

[0145] e eccentricity, under the WGS84 earth ellipsoid model, e 2 =0.006694379995;

[0146] N is the radius of the Maoyou circle;

[0147] β is the latitude of the scene matching feature point;

[0148] α is the longitude of the scene matching feature point;

[0149] S15, calculate the coordinates of the scene matching feature points relative to the aircraft in the earth coordinate system [△X e ,△Y e ,△Z e ] T .

[0150] When converting from the geographic system to the earth system, first rotate the latitude π / 2-β clockwise around the XE axis without moving, and then rotate the longitude π / 2+α clockwise around the ZS axis without moving. The coordinates of the scene matching feature points relative to the aircraft in the earth coordinate system [△X e ,△Y e ,△Z e ] T The calculation is as follows:

[0151]

[0152] S16. Calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T .

[0153] The coordinates of the scene matching feature points in the earth coordinate system [x e ,y e ,z e ] T , plus the coordinates of the scene matching feature points relative to the aircraft in the earth coordinate system [△X e ,△Y e ,△Z e ] T , we can get the coordinates of the aircraft in the earth system [X e ,Y e ,Z e ] T :

[0154]

[0155] When there are two or more scene matching feature points, two points are selected, scene matching feature point 1 and scene matching feature point 2, and the coordinate process of the aircraft in the earth coordinate system can be referred to as follows:

[0156] S21, calculate the coordinates [x e1 ,y e1 ,z e1 ] T and [x e2 ,ye2 ,z e2 ] T .

[0157]

[0158]

[0159] in,

[0160] h1 is the ellipsoid height of scene matching feature point 1;

[0161] β1 is the latitude of scene matching feature point 1;

[0162] α1 is the longitude of scene matching feature point 1;

[0163] h2 is the ellipsoid height of scene matching feature point 2;

[0164] β2 is the latitude of scene matching feature point 2;

[0165] α2 is the longitude of scene matching feature point 2.

[0166] S22, calculate the coordinates [x e12 ,y e12 ,z e12 ] T .

[0167]

[0168] S23, calculate the coordinates [X] of scene matching feature point 2 relative to scene matching feature point 1 in the geographic system. E12 ,Y N12 ,Z S12 ] T .

[0169]

[0170] S24, calculate the rotation angle (θ track +θ ac ).

[0171] The image coordinate system is based on the center of the imaging area scene O i is the origin, the rotation angle to the geographic coordinate system (θ track +θ ac ) is calculated as follows:

[0172]

[0173]

[0174] [X i12 ,Y i12 ,Z i12 ] T is the coordinate of scene matching feature point 2 relative to scene matching feature point 1 in the image coordinate system;

[0175] (nr1, na1) is the pixel coordinate of scene matching feature point 1;

[0176] (nr2, na2) is the pixel coordinate of scene matching feature point 2.

[0177] S25, calculate the coordinates of the scene matching feature point 1 relative to the aircraft in the geographic system [X E01 ,Y N01 ,Z S01 ] T .

[0178]

[0179]

[0180] in,

[0181] [X i1 ,Y i1 ,Z i1 ] T is the coordinate of scene matching feature point 1 in the image coordinate system.

[0182] S26, calculate the coordinates of the aircraft relative to the scene matching feature point 1 in the earth coordinate system [△X e1 ,△Y e1 ,△Z e1 ] T .

[0183] When converting from the geographic system to the earth system, first rotate the latitude π / 2-β clockwise around the XE axis without moving, and then rotate the longitude π / 2+α clockwise around the ZS axis without moving. The coordinates of the aircraft relative to the scene matching feature point 1 in the earth coordinate system [△X e1 ,△Y e1 ,△Z e1 ] T The calculation is as follows:

[0184]

[0185] S27, calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T .

[0186]

[0187] Step 3: Calculate the latitude and longitude coordinates of the aircraft based on the coordinates of the aircraft in the earth coordinate system to achieve the positioning of the aircraft.

[0188] Using the Earth coordinate system coordinates of the aircraft [X e ,Y e ,Z e ] T , calculate the latitude and longitude of the aircraft [α T ,β T ,H T ] T , please refer to the following:

[0189] Calculate the longitude α of the aircraft T :α T =arctan(Y e ,X e )……(19)

[0190] Using prior information for N, H T Assign an initial value and iterate the latitude β of the aircraft through equations (20) to (22) T , height H T , when the latitude β of the aircraft calculated in two consecutive iterations T When the difference is less than the set threshold 1e-10, the iteration stops and the latitude β of the aircraft is obtained. T , height H T :

[0191]

[0192]

[0193]

[0194] So far, the technical solution of the present application has been described in conjunction with the preferred embodiments shown in the accompanying drawings. Those skilled in the art should understand that the scope of protection of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the scope of protection of the present application.

Claims

1. An aircraft positioning method based on SAR image scene matching, characterized in that: include: Step 1: scene matching is performed between the real-time SAR image and the built-in reference image to obtain the pixel position and latitude and longitude coordinates of the scene matching feature points in the SAR image; Step 2: Calculate the coordinates of the aircraft in the earth coordinate system based on the pixel positions and longitude and latitude coordinates of the scene matching feature points; Step 3: The coordinates of the aircraft in the earth coordinate system are calculated to calculate the longitude and latitude coordinates of the aircraft and realize the positioning of the aircraft.

2. The method for aircraft positioning based on SAR image scene matching according to claim 1, characterized in that: In step 1, scene matching is performed between the real-time SAR image and the built-in reference image using a traditional image feature matching method or an image matching method based on deep learning.

3. The method for aircraft positioning based on SAR image scene matching according to claim 4, characterized in that: Reference images include high-precision digital maps, airborne / satellite-borne reference images, homologous / heterogeneous SAR images, and optical images.

4. The method for aircraft positioning based on SAR image scene matching according to claim 3, characterized in that: In step 2, when calculating the coordinates of the aircraft in the earth coordinate system based on the pixel position and latitude and longitude coordinates of the scene matching feature point, when there is only one scene matching feature point, calculating the coordinates of the aircraft in the earth coordinate system includes: S11, calculate the coordinates of the scene matching feature points in the image coordinate system [X i ,Y i ,Z i ] T : in, p r is the SAR image distance pixel size; p a is the SAR image azimuth pixel size; N r is the number of points in the range direction of the SAR image; N a is the number of SAR image azimuth points; (n r ,n a ) is the pixel position of the scene matching feature point; DirectionFlag is the SAR left / right viewing imaging direction; S12, calculate the coordinates of the scene matching feature points in the imaging coordinate system [X p ,Y p ,Z p ] T : in, θ ac is the imaging azimuth of the aperture center, -180o≤θ ac ≤180o, right side is considered as positive; H e is the height of the aircraft relative to the ground; R c is the action distance; S13, calculate the coordinates of the scene matching feature points relative to the aircraft in the geographic coordinate system [X E ,Y N ,Z S ] T : in, θ track is the track angle; S14, calculate the coordinates of the scene matching feature points in the earth coordinate system [x e ,y e ,z e ] T : in, R e is the equatorial plane radius; e eccentricity; N is the radius of the Maoyou circle; β is the latitude of the scene matching feature point; α is the longitude of the scene matching feature point; S15, calculate the coordinates of the scene matching feature points relative to the aircraft in the earth coordinate system [△X e ,△Y e ,△Z e ] T : S16. Calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T :

5. The method for aircraft positioning based on SAR image scene matching according to claim 4, characterized in that: In step 2, when calculating the coordinates of the aircraft in the earth coordinate system according to the pixel positions and latitude and longitude coordinates of the scene matching feature points, when there are two or more scene matching feature points, two points are selected, scene matching feature point 1 and scene matching feature point 2, to calculate the coordinates of the aircraft in the earth coordinate system, including: S21, calculate the coordinates [x e1 ,y e1 ,z e1 ] T and [x e2 ,y e2 ,z e2 ] T : in, h1 is the ellipsoid height of scene matching feature point 1; β1 is the latitude of scene matching feature point 1; α1 is the longitude of scene matching feature point 1; h2 is the ellipsoid height of scene matching feature point 2; β2 is the latitude of scene matching feature point 2; α2 is the longitude of scene matching feature point 2; S22, calculate the coordinates [x e12 ,y e12 ,z e12 ] T ; S23, calculate the coordinates [X] of scene matching feature point 2 relative to scene matching feature point 1 in the geographic system. E12 ,Y N12 ,Z S12 ] T : S24, calculate the rotation angle (θ track +θ ac ): [X i12 ,Y i12 ,Z i12 ] T is the coordinate of scene matching feature point 2 relative to scene matching feature point 1 in the image coordinate system; (nr1, na1) is the pixel coordinate of scene matching feature point 1; (nr2, na2) is the pixel coordinate of scene matching feature point 2; S25, calculate the coordinates of the scene matching feature point 1 relative to the aircraft in the geographic system [X E01 ,Y N01 ,Z S01 ] T : in, [X i1 ,Y i1 ,Z i1 ] T is the coordinate of scene matching feature point 1 in the image coordinate system; S26, calculate the coordinates of the aircraft relative to the scene matching feature point 1 in the earth coordinate system [△X e1 ,△Y e1 ,△Z e1 ] T : S27, calculate the coordinates of the aircraft in the earth coordinate system [X e ,Y e ,Z e ] T :

6. The method for aircraft positioning based on SAR image scene matching according to claim 5, characterized in that: R e = 6378137 m.

7. The method for aircraft positioning based on SAR image scene matching according to claim 6, characterized in that: e 2 ＝0.006694379995。 8. The method for aircraft positioning based on SAR image scene matching according to claim 7, characterized in that: In step 3, the longitude α of the aircraft is calculated from the coordinates of the aircraft in the earth coordinate system. T Calculated as: a T arctan(Y e ,X e )。 9. The method for aircraft positioning based on SAR image scene matching according to claim 8, characterized in that: In step 3, the coordinates of the aircraft in the earth coordinate system are used to calculate the latitude β of the aircraft in the latitude and longitude coordinates of the aircraft. T , height H T Calculated as: N, H T Assign initial value and iteratively calculate the latitude β of the aircraft T , height H T , when the latitude β of the aircraft calculated in two consecutive iterations T When the difference is less than the set threshold, the iteration stops and the latitude β of the aircraft is obtained. T , height H T , the iterative process is:

10. The method for aircraft positioning based on SAR image scene matching according to claim 9, characterized in that: Set the threshold to 1e-10.

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